Seat belt retractor

ABSTRACT

A seat belt retractor including a spool for winding up the seat belt, and a locking mechanism that prevents rotation of the spool. A belt withdrawal sensor actuates when the seat belt is withdrawn at a speed higher than a normal speed. The locking mechanism is actuated based on the actuation of the belt withdrawal sensor. A lock gear rotates with the spool when the locking mechanism is not in operation and rotates relative to the spool when the lock actuation mechanism is in operation. The lock gear actuates the locking mechanism by relative rotation between the lock gear and the spool. The belt withdrawal sensor is disposed on the lock gear allowing the belt withdrawal sensor to oscillate between an inoperative position and an operative position. An oscillation preventive member prevents the oscillation of the belt withdrawal sensor.

BACKGROUND

The present application relates generally to the field of a seat belt apparatus for restraining an occupant with a seat belt withdrawn from a seat belt retractor. More particularly, the present application relates to a seat belt retractor including at least a webbing sensor and that can prevent occurrence of an end lock when the seat belt is fully wound. Furthermore, the present application relates to a seat belt apparatus employing the aforementioned seat belt retractor.

Conventionally, a seat belt apparatus installed in a vehicle restrains an occupant in an emergency such as a crash, thereby preventing the occupants from being ejected out of their seats.

Such seat belt units generally include a seat belt retractor. Most conventional seat belt retractors are provided with a webbing sensor that oscillates by rapid withdrawal of the seat belt. The oscillation of the webbing sensor acts to prevent the seat belt from being withdrawn. The webbing sensor may oscillate to cause an end lock when the withdrawn seat belt is fully wound. The end lock can make normal withdrawal of the seat belt difficult.

SUMMARY

One embodiment of the disclosure relates to a seat belt retractor including a seat belt for restraining an occupant and a spool for winding up the seat belt. The seat belt retractor also includes a locking mechanism that allows the rotation of the spool when the locking mechanism is not in operation and prevents rotation of the spool in a belt withdrawing direction when the locking mechanism is in operation. The seat belt retractor also includes a belt withdrawal sensor that is actuated when the seat belt is withdrawn at a speed higher than a normal speed at a start of the withdrawal of the seat belt. The seat belt retractor also includes a lock actuation mechanism that actuates the locking mechanism based on the actuation of the belt withdrawal sensor. The lock actuation mechanism includes a lock gear that rotates together with the spool when the lock actuation mechanism is not in operation and rotates relative to the spool when the lock actuation mechanism is in operation. The lock gear actuates the locking mechanism by the relative rotation between the lock gear and the spool when the lock actuation mechanism is in operation. The belt withdrawal sensor is disposed on the lock gear allowing the belt withdrawal sensor to oscillate between an inoperative position where the belt withdrawal sensor allows the rotation of the lock gear both in the belt winding direction and the belt withdrawing direction and an operative position where the belt withdrawal sensor prevents the rotation of the lock gear at least in the belt withdrawing direction. The seatbelt retractor also includes an oscillation preventive member for preventing the oscillation of the belt withdrawal sensor and an oscillation preventive member control mechanism for controlling the movement of the oscillation preventive member. The oscillation preventive member is movable in a radial direction through a rotational center of the spool between an oscillation preventing position where the oscillation preventive member holds the belt withdrawal sensor at the inoperative position to prevent the belt withdrawal sensor from oscillating toward the operative position at least when the seat belt is fully or nearly fully wound and an oscillation allowing position where the oscillation preventive member allows the oscillation of the belt withdrawal sensor when a certain amount of the seat belt is withdrawn from the fully wound state. The oscillation preventive member control mechanism includes a movement control member that rotates at a speed lower than the speed of the spool to control the movement of the oscillation preventive member when the spool rotates.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present invention will become apparent from the following description, appended claims, and the accompanying exemplary embodiments shown in the drawings, which are briefly described below.

FIG. 1 is a schematic diagram showing a seat belt retractor, according to an exemplary embodiment.

FIG. 2 is a schematic diagram showing a seat belt retractor, according to an exemplary embodiment.

FIG. 3 is a perspective view of an ELR-ALR switching mechanism, an end lock preventive mechanism for a vehicle sensor, and an end lock preventive mechanism for a webbing sensor of the seat belt retractor, according to an exemplary embodiment.

FIGS. 4( a), 4(b) are illustrations showing the behavior of the webbing sensor of the seat belt retractor, according to an exemplary embodiment. FIG. 4( a) is an illustration of the webbing sensor in its inoperative state. FIG. 4( b) is an illustration of the webbing sensor in its operative state.

FIG. 5 is an illustration showing the ELR-ALR switching mechanism, the end lock preventive mechanism for the vehicle sensor, and the end lock preventive mechanism for the webbing sensor, according to exemplary embodiment.

FIGS. 6( a) and 6(b) are illustrations of the end lock preventive mechanism for the webbing sensor used in an exemplary embodiment. FIG. 6( a) is a schematic diagram of stoppers. FIG. 6( b) is a schematic diagram of cam grooves for controlling the stoppers.

FIGS. 7( a)-7(d) show a switching action from the ELR function mode to the ALR function mode used in the seat belt retractor of an exemplary embodiment.

FIGS. 8( a) and 8(b) show another part of the switching action from the ELR function mode to the ALR function mode used in the seat belt retractor of an exemplary embodiment.

FIGS. 9( a)-9(d) show a part of the action of the end lock preventive mechanism for the vehicle sensor, according to an exemplary embodiment.

FIGS. 10( a) and 10(b) show a further part of the action of the end lock preventive mechanism for the vehicle sensor, according to an exemplary embodiment.

FIGS. 11( a) and 11(b) show a part of the action of the end lock preventive mechanism for the fly wheel of an exemplary embodiment. FIGS. 11( c) and 11(d) show a part of the behavior of a pair of stoppers and cam grooves for controlling the action of the end lock preventive mechanism for the fly wheel of the embodiment.

FIGS. 12( a) and 12(b) show another part of the action of the end lock preventive mechanism for the fly wheel, according to an exemplary embodiment. FIGS. 12( c) and 12(d) show another part of the behavior of the pair of stoppers and the cam grooves for controlling the action of the end lock preventive mechanism for the fly wheel, according to an exemplary embodiment.

FIG. 13( a) shows a remaining part of the action of the end lock preventive mechanism for the fly wheel, according to an exemplary embodiment. FIG. 13( b) shows a remaining part of the behavior of the pair of stoppers and the cam grooves for controlling the action of the end lock preventive mechanism for the fly wheel, according to an exemplary embodiment.

FIG. 14 shows stoppers of an alternative exemplary embodiment.

DETAILED DESCRIPTION

According to one exemplary embodiment, a seat belt retractor can prevent an end lock due to a webbing sensor as disclosed in JP-A-09-058410m which is herein incorporated by reference in its entirety. A seat belt unit may include a cam plate that rotates according to the rotation of the spool for winding up a seat belt. A helical long groove is formed upon the cam plate. The seat belt retractor also includes an oscillation preventive member for preventing oscillation of the webbing sensor. The oscillation preventive member is arranged such that the oscillation preventive member is pivotally movable between a position for allowing oscillation of the webbing sensor and a position for preventing oscillation of the webbing sensor. The pivotal movement of the oscillation preventive member is controlled by a cam follower of the oscillation preventive member that is guided along the cam groove of the cam plate.

The pivotal movement of the oscillation preventive member may be controlled such that the oscillation preventive member is pivotally moved toward an oscillation allowing position. The oscillation preventive member is moved due to the rotation of the cam plate in the belt withdrawing direction. Furthermore, the oscillation preventive member is pivotally moved toward the oscillation preventing position when the cam plate is rotated in the belt winding direction. When the belt is fully wound, the oscillation preventive member is set to an oscillation preventing position. In the oscillation preventing position, the belt withdrawal sensor is not allowed to oscillate thereby preventing an end lock. When the fully wound seat belt is withdrawn by a predetermined amount, the oscillation preventive member is set at the oscillation allowing position. The belt withdrawal sensor is allowed to oscillate, preventing withdrawal of the seat belt when the seat belt is rapidly withdrawn.

The oscillation preventive member may rotate with the spool for withdrawing and winding the seat belt. The amount the oscillation preventive member rotates between the oscillation allowing position and the oscillation preventing position is small relative to the spool. The cam groove may be relatively long and may be formed with an increased number of helical circles. To increase the number of helical circles of the cam groove, the outer diameter of the cam plate can be increased. Therefore, the size of the seat belt retractor may be increased.

Diversification of vehicles generally results in diverse layouts of seat belt units. The range for forming the cam groove of the cam plate and the moving range of the oscillation preventive member may vary depending on the layout of the seat belt unit. Therefore, a large number of parts may be used to accommodate various layouts of the seat belt unit. However, in the case of a seat belt retractor having a large cam plate, it may be difficult to accommodate multiple layouts.

According to other exemplary embodiments, the seat belt retractor may be compact and effectively prevent an end lock due to a belt withdrawal sensor. The seat belt retractor may includes a mechanism for preventing an end lock. A seat belt unit may include the seat belt retractor.

According to an exemplary embodiment, a seat belt retractor includes a seat belt for restraining an occupant, a spool for winding up the seat belt, and a locking mechanism. The locking mechanism may allow rotation of the spool when the locking mechanism is not in operation, and may prevent rotation of the spool in the belt withdrawal direction when the locking mechanism is in operation. The seat belt retractor may further include a belt withdrawal sensor and a lock actuation mechanism. The belt withdrawal sensor may be actuated when the seat belt is withdrawn at a speed greater than a predetermined speed at the start of the withdrawal of the seat belt. The lock actuation mechanism may actuate a locking mechanism according to the actuation of the belt withdrawal sensor. The lock actuation mechanism includes at least a lock gear. The lock gear rotates with the spool when the lock actuation mechanism is not in operation, and rotates relative to the spool when the lock actuation mechanism is in operation. Furthermore, the lock gear may actuate the locking mechanism by the relative rotation between the lock gear and the spool when the lock actuation mechanism is in operation. A belt withdrawal sensor may be disposed on the lock gear such that the belt withdrawal sensor may oscillate between an inoperative position and an operative position. In the inoperative position, rotation of the lock gear in either direction is allowed. In the operative position, the belt withdrawal sensor may prevent the rotation of the lock gear at least in the belt withdrawing direction. The belt withdrawal sensor may include an oscillation preventive member and an oscillation preventive member control mechanism. The oscillation preventive member may be moved in a radial direction passing through the rotational center of the spool between an oscillation preventing position and an oscillation allowing position. In the oscillation preventing position the oscillation preventive member may hold the belt withdrawal sensor at the inoperative position. In the oscillation allowing position, the oscillation preventive member may allow oscillation of the belt withdrawal sensor. The oscillation preventive member control mechanism may also include a movement control member. The movement control member may rotate at a speed lower than that of the spool, thereby controlling movement of the oscillation preventive member when the spool rotates.

A seat belt retractor according to an exemplary embodiment includes an emergency locking mechanism and an automatic locking mechanism. The emergency locking mechanism may actuate when a deceleration larger than a predetermined deceleration is detected, thereby preventing the spool from rotating in the belt withdrawal direction. The automatic locking mechanism may actuate when the seat belt is fully withdrawn and may prevent withdrawal of a fully withdrawn seat belt until a predetermined amount of the seat belt is wound. Additionally, the seat belt retractor may include a lock switching mechanism for switching between an emergency locking function mode and an automatic locking function mode. The lock switching mechanism may include a switching lever. The switching lever may be set at either an emergency locking position where the emergency locking function mode may be set or an automatic locking position where the automatic locking function mode may be set. The lock switching mechanism may also include an eccentric gear that rotates at a speed lower than that of the spool when the spool rotates. The eccentric gear includes at least a switching lever control cam member for switching the setting position of the switching lever. The movement control member may include the eccentric gear. The oscillation preventive members movement may be controlled by the rotation of the eccentric gear, preventing the actuation of the belt withdrawal sensor when the seat belt is fully or nearly fully wound.

According to an exemplary embodiment, the belt withdrawal sensor of a seat belt retractor may include a ring member. The oscillation preventive member may include a plurality of stoppers that press the inner periphery of the ring member. As a result, actuation of the webbing sensor may be prevented when the seat belt is fully or nearly fully wound.

Furthermore, a seat belt retractor according to an embodiment may include a stopper biasing means for biasing the stopper in such a direction that the stoppers press the ring member.

According to an exemplary embodiment, a seat belt unit may include at least a seat belt for restraining an occupant, a tongue slidably supported by the seat belt, and a buckle that may be fixed to a vehicle floor or a vehicle seat and to which the tongue can be detachably latched. The seat belt unit may also include a seat belt retractor for performing at least one of winding up or withdrawal of a seat belt. The seat belt retractor may be actuated in the event of an emergency to prevent the withdrawal of the seat belt. Furthermore, the seat belt retractor may be a seat belt retractor as claimed in any one of claims 1 through 4.

In a seat belt retractor having the aforementioned structure, when the seat belt is fully or nearly fully wound, the oscillation preventive member may be moved by the movement control member. The oscillation preventive member may move in a radial direction that passes through the rotational center of the spool and may thus be set at the oscillation preventing position. Therefore, the oscillation of the belt withdrawal sensor may be prevented so that the belt withdrawal sensor is held at its inoperative position. Therefore, an end lock due to the belt withdrawal sensor can be prevented by a simple structure.

More particularly, since the movement control member is adapted to rotate at a reduced speed, the amount of rotation of the movement control member until the spool fully winds up the seat belt can be reduced. As a result, the movement control member may be of simple and compact construction.

The movement control member includes the eccentric gear of the lock switching mechanism. Furthermore, the eccentric gear is a flat member. Therefore, the compact design of the movement control member may be more easily achieved. In addition, since the eccentric gear of the lock switching mechanism may be used as the movement control member, an exclusive control member for controlling the oscillation preventive member is not required. Accordingly, the parts count of the seat belt retractor of the automatic locking type can be reduced, even with the function of preventing an end lock due to the belt withdrawal sensor.

Further, since the belt withdrawal sensor is provided with the ring member and the oscillation preventive member is composed of stoppers, a conventional belt withdrawal sensor can be employed without significant design change. Therefore, a further simple structure is achieved because all that is required is to simply press the ring member by the stoppers. In addition, since the oscillation preventive member includes the stoppers that are of simple structure, the seat belt retractor can be flexibly and inexpensively adapted to various layouts of seat belt units. Additionally, the seat belt retractor may require fewer parts by suitably setting the movement distance of the stoppers relative to the eccentric gear.

Furthermore, the stoppers may be biased in a direction pressing the ring member by using a stopper biasing method. Therefore, the ring member of the belt withdrawal sensor can be locked with larger force.

According to an exemplary embodiment, end locks in the seat belt retractor can be effectively prevented, thereby improving the operability of the seat belt and enabling smooth and stable operation by the occupant.

Hereafter, the preferred embodiments for carrying out the present disclosure will be described with reference to the attached drawings.

FIG. 1 is a schematic diagram of a seat belt apparatus including a seat belt retractor according to an exemplary embodiment.

As shown in FIG. 1, the seat belt unit 1 may include, similar to a known seat belt unit, a seat belt retractor 3 and a seat belt 4. The seat belt retractor 3 may be fixed to a vehicle body near a vehicle seat 2, and the seat belt 4 may be withdrawn from the seat belt retractor 3. The seat belt 4 includes a belt anchor 4 a fixed to a vehicle floor or the vehicle seat 2. The seat belt unit 1 may also include a deflection fitting 5 for guiding a seat belt 4 toward an occupant's shoulder, and a tongue 6 slidably supported by the seat belt 4. Additionally, a buckle 7 may be fixed to the vehicle floor or the vehicle seat 2 such that the tongue 6 can be inserted and detachably latched.

The seat belt retractor 3 of the embodiment includes a U-like frame 8 (that may be similar to conventional seat belt retractors) that includes a back wall 8 a and left and right side walls 8 b, 8 c. The left and right side walls 8 b, 8 c project from edges of the back wall 8 a in a direction perpendicular to the extending direction of the back wall 8 a as shown in FIG. 2.

A spool 9 that the seat belt 4 is wound on may be inserted through circular holes formed in side walls 8 b, 8 c of the frame 8 such that the spool 9 is rotatably disposed. The spool 9 includes a first spool section 9 a and a second spool section 9 b that may be coaxially and rotatably fitted into a left end portion of the first spool portion 9 a. The first spool section 9 a includes a belt winding portion 9 a 1, a flange portion 9 a 2 formed at the right end of the belt winding portion 9 a 1, and a rotary shaft 9 a 3 extending from the flange portion 9 a 2 in the axial direction. The second spool section 9 b includes a flange portion 9 b 1 and a rotary shaft 9 b 2 that extends from the flange portion 9 b 1 in the axial direction.

An end portion 9 a 4 of the rotary shaft 9 a 3 of the first spool section 9 a may be supported by a cover 52 fixed to the side wall 8 c via a bush 50 such that the rotary shaft 9 a 3 rotates with the bush 50. A lock gear 11 may be coaxially fitted to the rotary shaft 9 a 3. Thus, similar to a conventional lock gear 11, the lock gear 11 rotates together with the rotary shaft 9 a 3 when the lock gear 11 is not prevented from rotating. The rotary shaft 9 a 3 rotates relative to the lock gear 11 when the lock gear 11 is prevented from rotating. As shown in FIG. 3, the lock gear 11 includes a predetermined number of ratchet teeth 11 a that may be formed on the outer periphery of the lock gear 11 and in an annular shape. Additionally, a cam hole 11 b may be formed in a side surface of the lock gear 11.

As shown in FIG. 2 and FIG. 3, a fly wheel 12 is oscillatably supported by the lock gear 11. The fly wheel 12 may be an inertia member composing the belt withdrawal sensor. The fly wheel 12 of includes an inertial mass portion 12 a and a ring portion 12 b. The inertial mass portion 12 a includes a through hole 12 d that a projecting pin 11 c formed on the lock gear 11 may be fitted such that the fly wheel 12 is oscillatably supported. An engaging claw 12 c may be formed upon the inertial mass portion 12 a. The ring portion 12 b may be formed in an annular shape as shown in FIGS. 4( a), 4(b), and FIG. 5.

An eccentric disk 13 may be fitted and fixed to the rotary shaft 9 a 3 of the first spool section 9 a. An eccentric gear 14 may be supported on the eccentric disk 13 such that the eccentric gear 14 is rotatable relative to the eccentric disk 13.

The eccentric gear 14 includes a predetermined number of external teeth 14 a. The external teeth 14 a can mesh with internal teeth 15 a of a ring gear 15. The ring gear 15 may be formed in the casing 10 coaxially with the spool 9. The outer diameter of the spool may be larger than the outer diameter of the eccentric gear 14. The eccentric gear 14 includes a first lever operation cam 16, a second lever operation cam 17, and a third lever operation cam 18.

As shown in FIG. 3 and FIG. 4( a), rotatably supported on the casing 10 may be a switching lever 19. The switching lever 19 includes an engaging lever 20 and a disengaging lever 21. The switching lever 19 also includes a projection 22 and an engaging arm 23 projecting toward the disengaging lever 21. The projection 22 may be engaged with either one of two first and second concavities 24 a, 24 b as curves respectively formed in a switching lever position control spring 24. The position control spring 24 may include a plate spring, thereby positioning the switching lever 19.

When the projection 22 engages the first concavity 24 a, the switching lever 19 may be placed and held at such a position that the engaging lever 20 may contact the first lever operation cam 16. The engaging arm 23 may be set at such a position such that the engaging arm 23 may not engage with any one of the ratchet teeth 11 a of the lock gear 11. Additionally, the seat belt retractor 3 may be set in a state such that the seat belt retractor 3 exercises the ELR function. When the projection 22 is engaged with the second concavity 24 b, the switching lever 19 may be placed and held at a position such that the disengaging lever 21 may contact the second lever operation cam 17. Therefore, the engaging arm 23 may be set at a position such that the engaging arm 23 may engage one of the ratchet teeth 11 a when the lock gear 11 rotates in the belt withdrawing direction. Then, the engaging arm 23 may engage one of the ratchet teeth 11 a by the rotation of the lock gear 11 in the belt withdrawing direction. Thus, rotation of the spool 9 in the belt withdrawing direction may be prevented. Accordingly, the seat belt retractor 3 may be set in a state such that the retractor 3 exercises the ALR function.

The eccentric disk 13, the eccentric gear 14, the ring gear 15, the first lever operation cam 16, the second lever operation cam 17, the switching lever 19, and the switching lever position control spring 24 operate together to function as an ELR-ALR switching mechanism 25. Detailed structure and detailed operation of the ELR-ALR switching mechanism 25 are described in the publication JP-A-2004-262447 and thus can be readily understood with reference to the publication. Therefore, these will be omitted.

Similar to conventional webbing sensors, the fly wheel 12 may be arranged such that the engaging claw 12 c can engage any one of the predetermined number of the ratchet teeth 26. Therefore, when the seat belt retractor 3 is not in operation (e.g., the seat belt 4 is fully wound) and the seat belt 4 is withdrawn faster than a predetermined speed, the fly wheel 12 may rotate together with the lock gear 11. As a result, the fly wheel 12 may be held at a position shown in FIG. 4( a) such that the engaging claw 12 c may not engage with the ratchet wheel 26. When the seat belt 4 withdrawn at a relatively large acceleration exceeding the aforementioned predetermined value, the fly wheel 12 may oscillate relative to the rotation of the lock gear 11 due to inertial delay of the inertial mass portion 12 a. The fly wheel 12 may be set at a position shown in FIG. 4( b) such that the engaging claw 12 c may engage one of the ratchet teeth 26. Therefore, when the seat belt 4 is rapidly withdrawn, the rotation of the spool 9 in the belt withdrawing direction may be prevented so as to not allow the withdrawal of the seat belt 4.

Furthermore, as shown in FIG. 2 and FIG. 3, a vehicle sensor 27 may be used as a deceleration detecting mechanism and may be attached to the side wall 8 c. The vehicle sensor 27 may be a conventional vehicle sensor and may include an inertia ball 28. The inertial ball 28 may be actuated when a large deceleration is applied to the vehicle such as the event of a vehicle collision. A casing 29 may be attached to the side wall 8 c to support the inertia ball 28. An actuator 30 may be pivotally mounted to the casing 29 and may be actuated by the actuation of the inertia ball 28. A cover 31 may be attached to the casing 29. The actuator 30 includes an engaging claw 30 a. When the inertia ball 28 is not actuated, the engaging claw 30 a may be held at a position such that the engaging claw 30 a may not engage any of the ratchet teeth 11 a of the lock gear 11. When the inertia ball 28 is actuated, the engaging claw 30 a may be set at a position such that the engaging claw 30 a may engage one of the ratchet teeth 11 a. When the engaging claw 30 a is not engaged with any one of the ratchet teeth 11 a, the lock gear 11 may rotate in both the belt winding direction and the belt withdrawing direction. When the engaging claw 30 a is engaged with one of the ratchet teeth 11 a, the lock gear 11 may be prevented from rotating in the belt withdrawing direction.

Disposed on the side wall 8 b may be a conventional pretensioner 32. The rotary shaft 9 b 2 of the second spool section 9 b may be rotatably supported by a casing 33 for the pretensioner 32. The pretensioner 32 may be actuated in the event of an emergency. The operational force of the pretensioner 32 may be transmitted to the second spool section 9 b such that the spool 9 rotates in the belt winding direction. Therefore, the seat belt 4 may be wound up at an early stage of the emergency, thereby increasing the belt tension.

Rotatably supported by the second spool section 9 b may be a conventional pawl 34. The pawl 34 may engage with one of a predetermined number of teeth 35, that may be formed in the inner periphery of the side wall 8 b. When the first spool section 9 a and the lock gear 11 rotate in the belt withdrawing direction, the pawl 34 may be held at a position such that the pawl 34 may not engage any one of the teeth 35. When the first spool section 9 a rotates in the belt withdrawing direction relative to the lock gear 11, the pawl 34 may be set by a control member (not shown). The control member may be controlled by a cam hole 11 b of the lock gear 11 at a position such that the pawl 34 may not engage one of the teeth 35. When the pawl 34 is not engaged with the teeth 35, the second spool section 9 b may rotate in both the belt winding direction and the belt withdrawing direction. When the pawl 34 is engaged with one of the teeth 35, the second spool section 9 b may not rotate at least in the belt withdrawing direction. The pawl 34 and the teeth 35 work together to function as a locking mechanism of the present disclosure. The lock gear 11 may include a lock actuation mechanism of the present disclosure. The operation control of the pawl 34 by the control member and the cam hole 11 b is conventionally known and easily structure. Additionally, these are not characterizing portions of the present disclosure even though they are components of the present disclosure. Therefore, the detailed descriptions thereof will be omitted.

As shown in FIG. 2, a conventional torsion bar 36 may be disposed to extend between the first and second spool sections 9 a, 9 b. Shown in FIG. 2, the right end portion 36 a of the torsion bar 36 may be adapted to rotate with the first spool section 9 a. Also shown in FIG. 2, the left end portion 36 b of the torsion bar 36 may be adapted to rotate together with the second spool section 9 b.

In the event of an emergency, the pawl 34 may engage one of the teeth 35, thus preventing the second spool section 9 b from rotating in the belt withdrawing direction. Due to the inertia of the occupant, the seat belt 4 may be withdrawn and the first spool section 9 a may begin to rotate in the belt withdrawing direction. The torsion bar 36 may torsionally deform so as to absorb impact energy applied to the occupant by the seat belt 4.

The seat belt retractor 3 is provided with an end lock preventive mechanism for preventing an end lock as mentioned above which may occur due to the operation of the actuator 30 of the vehicle sensor 27 or the operation of the fly wheel 12 of the webbing sensor.

As shown in FIG. 3 and FIG. 5, the end lock preventive mechanism 37 for the vehicle sensor 27 includes an end lock preventive lever 38 and an end lock preventive lever position control spring 39. The end lock preventive lever control spring 39 includes a plate spring, an eccentric ring 13, and an eccentric gear 14.

The end lock preventive lever 38 may be rotatably supported on the casing 10. The end lock preventive lever 38 includes a locking lever 40 and an unlocking lever 41. The end lock preventive lever 38 also includes a projection 42 and an end lock preventive arm 43. The projection 42 may engage the first and/or second concavities 39 a, 39 b as curves formed in an end lock preventive lever position control spring 39. Therefore, the end lock preventive lever 38 may be positioned.

As shown in FIG. 5, when the projection 42 engages the first concavity 39 a, the end lock preventive lever 38 may be held at a position such that the third lever operation cam 18 may contact the locking lever 40 and may not contact the unlocking lever 41. As a result, the end lock preventive arm 43 may be set at an end lock prevention canceling position shown by a solid line in FIG. 5 and the actuator 30 of the vehicle sensor 27 may be set to an operable state. When the projection 42 is engages the second concavity 39 b, the end lock preventive lever 38 may be positioned and held such that the third lever operation cam 18 may contact the unlocking lever 41 and may not contact the locking lever 40. Therefore, the end lock preventive arm 43 may be set at an end lock preventing position shown by a two-dot chain line in FIG. 5. In the end lock preventing position, the end lock preventive arm 43 may contact the actuator 30 of the vehicle sensor 27, thereby locking the actuator 30 at an inoperable position. Accordingly, the actuator 30 may be set in an inoperable state.

As shown in FIG. 3 and FIGS. 6( a), 6(b), an end lock preventive mechanism 44 for the fly wheel 12 as the webbing sensor includes a pair of stoppers 45, 46, a ring portion 12 b of the fly wheel 12, an eccentric ring 13, an eccentric gear 14, a pair of guide grooves 47, 48, and a cam groove 49. The pair of guide grooves 47, 48 may be spaced from each other in a circumferential direction by an angle 180°. Therefore, the pair of guide grooves 47,48 may oppose each other and extend linearly. Additionally, the cam groove 49 may be formed in the casing 10.

The pair of stoppers 45, 46 may be formed in a similar configuration. Each stopper includes a contact portion 45 a, 46 a that may contact the inner periphery of the ring portion 12 b of the fly wheel 12. A guided portion 45 b, 46 b may be guided to move along one of the pair of guide grooves 47, 48. A cam follower 45 c, 46 c may move along the cam groove 49.

The guide grooves 47, 48 of the eccentric gear 14 may guide the stoppers 45, 46 such that the guided portions 45 b, 46 b of the stoppers 45, 46 move in the radial direction of the eccentric gear 17. The stoppers 45, 46 include an oscillation preventive member according to the present disclosure.

The cam groove 49 may include a pair of small-diameter circular grooves 49 a, 49 b that may be coaxial with a circular hole 10 a of the casing 10. The bush 50 may pass through the circular hole 10 a. Additionally, there may be a pair of large-diameter circular grooves 49 c, 49 d that may be coaxial with the circular hole 10 a. The small-diameter circular grooves 49 a, 49 b and the large-diameter circular grooves 49 c, 49 d may form a closed loop. When arranged in a closed loop, the pair of small-diameter circular grooves 49 a, 49 b and the pair of large-diameter circular grooves 49 c, 49 d may be alternately arranged in a circumferential direction of the circular hole 10 a. The lengths in the circumferential direction of the pair of small-diameter circular grooves 49 a, 49 b may be equal to each other. The lengths in the circumferential direction of the pair of large-diameter circular grooves 49 c, 49 d may be equal to each other and shorter than the lengths in the circumferential direction of the small-diameter circular grooves 49 a, 49 b. The cam groove 49 may be formed of an endless-type inner peripheral wall 49 e and an endless-type outer peripheral wall 49 f. The endless-type outer peripheral wall 49 f may extend from the side wall of the casing 10 in the axial direction of the spool 9.

The cam follower 45 c of the stopper 45 may be positioned within the large-diameter circular groove 49 c when the seat belt 4 is fully wound. The contact portion 45 a may contact the inner periphery of the ring portion 12 b, thereby pressing the ring portion 12 b in the outer radial direction.

Similarly, the cam follower 46 c of the other stopper 46 may be positioned within the large-diameter circular groove 49 d when the seat belt 4 is fully wound. The contact portion 46 a may contact the inner periphery of the ring portion 12 b, thereby pressing the ring portion 12 b in the outer radial direction.

Furthermore, the cam follower 45 c may be positioned within the small-diameter circular groove 49 a when the other cam follower 46 c is positioned within the other small-diameter circular groove 49 b. Additionally, the cam follower 45 c may be positioned within the large-diameter circular groove 49 c when the other cam follower 46 c is positioned within the other large-diameter circular groove 49 d. More particularly, the positions of the pair of cam followers 45 c, 46 c may be controlled in synchronization with each other. Therefore, the contact portions 45 a, 46 a of the pair of stoppers 45, 46 may contact the inner periphery of the ring portion 12 b thereby pressing the inner periphery in the outer radial direction simultaneously. Since the inner periphery of the ring portion 12 b may be pressed by the contact portions 45 a, 46 a, the fly wheel 12 may be set in a locked state where the fly wheel 12 can not oscillate. The eccentric gear 14, the guide grooves 47, 48, and the cam groove 49 may work together to function as an oscillation preventive member control mechanism according to the present disclosure.

A conventional spring mechanism 51 may be attached to the casing 10. The biasing force of the spring mechanism 51 may be transmitted to the spool 9 via the bush 50. As a result, the spring mechanism 51 may bias the spool 9 in the belt winding direction. Due to the biasing force of the spring mechanism 51, the seat belt 4 may be fully wound onto the spool 9 when the seat belt is not used.

Hereafter, respective actions of the ELR-ALR switching mechanism 25, the end lock preventive mechanism 37 for the vehicle sensor 27, and the end lock preventive mechanism 44 for the fly wheel 12 will be described.

FIGS. 7( a)-7(d) and FIGS. 8( a)-8(b) show the switching actions from the ELR function mode to the ALR function mode. FIGS. 9( a)-9(d) and FIGS. 10( a) and 10(b) are illustrations for showing the actions of the end lock preventive mechanism 37 for the vehicle sensor 27. FIGS. 11( a) and 11(b), FIGS. 12( a) and 12(b), and FIG. 13( a) are illustrations for showing the actions of the end lock preventive mechanism 44 for the fly wheel 12. FIGS. 11( c) and 11(d), FIGS. 12( c) and 12(d), and FIG. 13( b) are illustrations for explaining respective behaviors of the pair of stoppers 45, 46 and the cam groove 49 for controlling the actions of the end lock preventive mechanism 44 for the fly wheel 12.

When the seat belt 4 is fully wound by the seat belt retractor 3, the seat belt retractor 3 may be set by the ELR-ALR switching mechanism 25 in a state such that the seat belt retractor 3 can exercise the ELR mechanism. The switching lever 19 may be positioned such that the projection 22 may engage the first concavity 24 a of the switching lever position control spring 24 as shown in FIG. 7( a). When the switching lever 19 is in this position, the first lever operation cam 16 may contact the engaging lever 20 according to the position of the eccentric gear 14. Additionally, the first lever operation cam 16 may not contact the disengaging lever 21. Furthermore, the second lever operation cam 17 may not contact the engaging lever 20 and/or the disengaging lever 21.

As shown in FIG. 9( a), the end lock preventive lever 38 may be positioned such that the projection 42 may engage the second concavity 39 b of the end lock preventive lever position control spring 39. When the end lock preventive lever 38 is in this position, the third lever operation cam 18 may contact the unlocking lever 41 according to the position of the eccentric gear 14. Additionally, the third lever operation cam 18 may not contact the locking lever 40. Therefore, the end lock preventive arm 43 of the end lock preventive lever 38 may be set at an end lock preventing position such that the actuator 30 enters an inoperative state.

The contact portions 45 a, 46 a of the pair of stoppers 45, 46 of the end lock preventive mechanism 44 may not press the inner periphery of the ring portion 12 b of the fly wheel 12.

As the seat belt 4 begins to be withdrawn from the seat belt retractor 3, the eccentric gear 14 may eccentrically rotate at a reduced speed in the belt winding direction. Therefore, as shown in FIG. 11( c), the cam followers 45 c, 46 c of the pair of stoppers 45, 46 may enter the large-diameter circular grooves 49 c, 49 d. As shown in FIG. 11( a), the respective contact portions 45 a, 46 a may press the inner periphery of the ring portion 12 b such that the fly wheel 12 may be locked from oscillating. Thus, the fly wheel 12 may enter an inoperable state.

As the seat belt 4 is further withdrawn, the pair of cam followers 45 c, 46 c may rotate in the belt winding direction. As shown in FIG. 11( d), the cam followers 45 c, 46 c may reach the ends of the large-diameter circular grooves 49 c, 49 d. As shown in FIG. 11( b), when the cam followers 45 c, 46 c are positioned within the large-diameter circular grooves 49 c, 49 d, the contact portions 45 a, 46 a may continue pressing the ring portion 12 b. Therefore, a lock of the fly wheel 12 may be maintained.

As the seat belt 4 is further withdrawn, the pair of cam followers 45 c, 46 c may further rotate in the belt winding direction. As a result, the cam followers 45 c, 46 c may disengage the large-diameter circular grooves 49 c, 49 d and engage the small-diameter circular grooves 49 a, 49 b as shown in FIG. 12( c). Accordingly, as shown in FIG. 12( a), the contact portions 45 a, 46 a may move apart from the inner periphery of the ring portion 12 b such that the lock of the fly wheel 12 is cancelled. Therefore, the fly wheel 12 may oscillate and enter an operable state.

The rotational angle of the eccentric gear 14 from when the seat belt 4 is fully wound state to when the cam followers 45 c, 46 c enter the small-diameter circular grooves 49 a, 49 b is about 60°. Therefore, the amount of seat belt 4 withdrawn is slight. By the withdrawal of a slight amount of the seat belt 4 from the fully wound state, the fly wheel 12 may switch from an inoperable state to an operable state. The fly wheel 12 can exercise the same function as a conventional webbing sensor. Accordingly, when the seat belt 4 is withdrawn at a speed higher than a predetermined belt withdrawal speed, the fly wheel 12 may be actuated. As a result, the engaging claw 12 c may engage one of the ratchet teeth 26, thereby preventing the lock gear 11 from rotating in the belt withdrawing direction. Therefore, since the spool 9 rotates relative to the lock gear 11 in the belt withdrawing direction, the pawl 34 may engage one of the internal teeth 35 of the side wall 8 b. Thus, the second spool section 9 b may be prevented from rotating in the belt withdrawing direction. As a result, the withdrawal of the seat belt 4 is prevented.

As shown in FIG. 9( b), when the pair of cam followers 45 c, 46 c enter the small-diameter circular grooves 49 a, 49 b, the third lever operation cam 18 may contact the unlocking lever 41 of the end lock preventive lever 38. As the seat belt 4 is further withdrawn, the third lever operation cam 18 may press the unlocking lever 41 as shown in FIG. 9( c). Thus, the end lock preventive lever 38 may be pivotally moved so that the projection 42 may disengage the second concavity 39 b of the end lock preventive lever position control spring 39 and may engage the first concavity 39 a. Therefore, the end lock preventive arm 43 of the end lock preventive lever 38 may be set and held at the end lock prevention cancelling position such that the actuator 30 of the vehicle sensor 27 enters an operable state. Similar to a conventional vehicle sensor, the actuator 30 may be actuated by movement of the inertia ball 28 in the event of an emergency where a large deceleration is applied to the vehicle. Thus, the engaging claw 30 a may engage one of the ratchet teeth 11 a of the lock gear 11. Due to rotation of the lock gear 11 in the belt withdrawing direction, one of the ratchet teeth 11 a may engage the engaging claw 30 a. Therefore, the lock gear 11 may be prevented from rotating in the belt withdrawing direction. As a result, since the spool 9 rotates relative to the lock gear 11 in the belt withdrawing direction, the pawl 34 may engage one of the internal teeth 35 of the side wall 8 b. As a result, the second spool section 9 b may be prevented from rotating in the belt withdrawing direction. FIG. 9( c) shows the actuator 30 in an operative state.

Since the first spool section 9 a further rotates in the belt withdrawing direction as the seat belt 4 is withdrawn by inertia of the occupant, the torsion bar 36 may torsionally deform similar to a conventional torsion bar. The torsional deformation of the torsion bar 36 absorbs impact energy applied to the occupant by the seat belt 4.

As the seat belt 4 withdraws further, the third lever operation cam 18 may pass through the end lock preventive lever 38 as shown in FIG. 12( b). The end lock preventive lever 38 may be held at the end lock prevention cancelling position such that the vehicle sensor 27 maintains an operable state. As shown in FIG. 12( d), the pair of cam followers 45 c, 46 c may further rotate in the belt winding direction, entering the small-diameter circular grooves 49 a, 49 b. Therefore, as shown in FIG. 12( b), the contact portion 45 a may be held in a position apart from the inner periphery of the ring portion 12 b. As a result, the fly wheel 12 may maintain an operable state.

As the seat belt 4 withdraws further, the eccentric gear 14 may rotate in the belt winding direction. Additionally, the first lever operation cam 16 may move towards the engaging lever 20 of the switching lever 19. Meanwhile, the vehicle sensor 27 and the fly wheel 12 maintain their operable states.

Before the seat belt 4 is fully withdrawn, as shown in FIG. 7( b), the first lever operation cam 16 may contact and press the engaging lever 20 of the switching lever 19. As shown in FIG. 7( c), the switching lever 19 may pivotally move such that the projection 22 of the switching lever 19 engages the second concavity 24 b of the switching lever position control spring 24. Accordingly, the switching lever 19 may be positioned. More particularly, the engaging arm 23 of the switching lever 19 may be held at a position such that the engaging arm 23 may engage the ratchet teeth 11 a of the lock gear 1. Accordingly, the seat belt retractor 3 may be switched from the ELR function mode to the ALR function mode.

As the seat belt 4 is fully withdrawn, as shown in FIG. 7( d), one of the ratchet teeth 11 a of the lock gear 11 engage the engaging arm 23. Additionally, the vehicle sensor 27 may maintain an operable state as shown in FIG. 9( d). The cam followers 45 c, 46 c of the stoppers 45, 46 may be positioned at an end of the small-diameter circular grooves 49 a, 49 b on the side of the large-diameter circular grooves 49 c, 49 d, as shown in FIG. 13( b). The contact portions 45 a, 46 a may be spaced apart from the inner periphery of the ring portion 12 b as shown in FIG. 13( a). Therefore, the fly wheel 12 may maintain an operable state.

As the spool 9 rotates in the belt winding direction from a state that the seat belt 4 is fully withdrawn, a certain amount of the seat belt 4 may be wound onto the spool 9. The lock gear 11 may also rotate in the belt winding direction. When the lock gear 11 rotates in the belt winding direction, the engaging arm 23 slides on the ratchet teeth 11 a and may not engage the ratchet teeth 11 a. Therefore, the seat belt 4 may be smoothly wound onto the spool 9. If an attempt is made to withdraw the seat belt 4 after a predetermined amount of the seat belt 4 is wound, both the spool 9 and the lock gear 11 may rotate in the belt withdrawing direction. As the spool 9 and lock gear 11 rotate in the belt withdrawing direction, one of the ratchet teeth 11 a of the lock gear 11 may engage the engaging arm 23. Therefore, the spool 9 and the lock gear 11 may be prevented from rotating in the belt withdrawing direction such that the seat belt 4 may not be withdrawn. The seat belt retractor 3 exercises the ALR function. Due to rotation of the spool 9 in the belt winding direction, the eccentric gear 14 nay rotate in the belt withdrawing direction.

As the seat belt 4 is further wound, the third lever operation cam 18 may gradually come closer to the locking lever 40 of the end lock preventive lever 38. As shown in FIG. 10( a), by further winding of the seat belt 4 the third lever operation cam 18 may contact and press the locking lever 40. Then, as shown in FIG. 10( b), the end lock preventive lever 38 may pivotally move such that the projection 42 of the end lock preventive lever 38 may disengage the first concavity 39 a and may engage the second concavity 39 b of the end lock preventive lever position control spring 39. Therefore, the end lock preventive arm 43 of the end lock preventive lever 38 may be set and held at the end lock preventing position such that the actuator 30 of the vehicle sensor 27 enters an inoperable state. Since the seat belt retractor 3 is set in the ALR function mode, withdrawal of the seat belt 4 may be prevented in the event of an emergency.

As the seat belt 4 is further wound and nears being fully wound, the second lever operation cam 17 may contact and press the disengaging lever 21 of the switching lever 19. As shown in FIG. 8( b), the switching lever 19 may be pivotally moved such that the projection 22 of the switching lever 19 may disengage the second concavity 24 b and may engage the first concavity 24 a of the switching lever position control spring 24. Therefore, the engaging arm 23 may be set at a position such that the engaging arm 23 may not engage the ratchet teeth 11 a of the lock gear 11. Accordingly, the seat belt retractor 3 may be switched from the ALR function mode to the ELR function mode.

As shown in FIG. 11( d), as the seat belt 4 is further wound, the cam followers 45 c, 46 c of the stoppers 45, 46 may enter the large-diameter circular grooves 49 c, 49 d from the small-diameter circular grooves 49 a, 49 b. Therefore, the contact portions 45 a, 46 a may contact and press the inner periphery of the ring portion 12 b, locking the fly wheel 12 so that the fly wheel 12 enters an inoperable state.

As the seat belt 4 is fully wound, the rotation of the spool 9 may be stopped and the rotation of the eccentric gear 14 may also be stopped while the vehicle sensor 27 and the fly wheel 12 enter inoperable states.

When the seat belt is fully or nearly fully wound, the pair of stoppers 45, 46 may move in a radial direction passing through the rotational center of the spool 4. The stoppers 45, 46 are thus set at the oscillation preventing position where the stoppers 45, 46 may press the inner periphery of the ring portion 12 b. Therefore, the oscillation of the fly wheel 12 of the webbing sensor may be prevented so that the fly wheel 12 may be held at an inoperative position. Additionally, an end lock due to the webbing sensor can be prevented by a simple structure including the stoppers 45, 46.

The eccentric gear 14 may be used as a movement control member for controlling the pair of stoppers 45, 46. The pair of stoppers 45, 46 may move between an oscillation preventing position and an oscillation allowing position. In the oscillation preventing position, the stoppers 45, 46 may press the inner periphery of the ring portion 12 b. In the oscillation allowing position, the stoppers 45, 46 may not press the inner periphery of the ring portion 12 b. Therefore, the structure for controlling the actuation of the stoppers may be made both simpler and more compact.

The eccentric gear 14 may be a flat member. Therefore, a compact design of the movement control member can be further effectively achieved. Additionally, an exclusive control member for controlling the pair of stoppers 45, 46 is not required. Accordingly, the parts count of the seat belt retractor of the automatic locking type can be reduced, even with the function of preventing an end lock due to the webbing sensor.

Further, the fly wheel 12 may be included with the ring portion 12 b, and the inner periphery of the ring portion 12 b may be pressed by the stoppers 45, 46 thereby preventing actuation of the fly wheel 12. Thus, a conventional fly wheel 12 can be employed without significant design change. Additionally, the oscillation preventive mechanism may be a simple structure since all that is required is to simply press the ring portion 12 b by the stoppers 45, 46. In addition, since the stoppers 45, 46 are used, the seat belt retractor can be flexibly and inexpensively adapted to various layouts of seat belt units 1. The various layouts may require a lower parts count by suitably setting the movement distance of the stoppers 45, 46 relative to the eccentric gear 14.

Therefore, end locks in the seat belt retractor 3 can be effectively prevented and operability of the seat belt 4 by the occupant may be improved.

Although the end lock preventive mechanism 44 may be provided with the pair of stoppers 45, 46 and the pair of the guide grooves 47, 48, the present disclosure is not limited thereto. For example, two or more stoppers for pressing the ring portion 12 b and two or more guide grooves for guiding the stoppers may be included. The respective stoppers and the respective guide grooves may be formed at any positions in the circumferential direction of the eccentric gear 14. However, it is preferable to dispose the stoppers and the guide grooves at equal spaces in the circumferential direction of the eccentric gear 14. Then, the ring portion 12 b may be pressed equally along the circumferential direction.

Additionally, as shown in FIG. 14, the pair of stoppers 45, 46 may be adapted to press in outward radial directions α, β relative to the eccentric gear 14 by an elastic biasing member 53. Accordingly, the ring portion 12 b of the fly wheel 12 can be locked by a larger force. Therefore, the pair of stoppers 45, 46 and the elastic biasing member 53 may be integrally formed from a resin or a metal. Alternatively, the pair of stoppers 45, 46 and the elastic biasing member 53 may be formed separately and the pair of stoppers may be connected by the elastic biasing member 53.

Although both of the two end lock preventive mechanisms 37, 44 are included in the seat belt retractor of the aforementioned embodiment, only the end lock preventive mechanism 44 for preventing an end lock due to the fly wheel 12 may be included.

The present disclosure is not limited to a seat belt retractor including the ELR function and the ALR function as in the aforementioned embodiments. The present disclosure can be adapted to a seat belt retractor having only the ELR function. Furthermore, the aforementioned embodiments are just illustrative examples for carrying out the seat belt retractor of the present disclosure. Therefore, the respective components of the seat belt retractor may be vary within a scope of claims of the present invention.

The seat belt retractor and the seat belt apparatus of the present disclosure are suitably used as a seat belt retractor in that an end lock due to a belt withdrawal sensor may occur, and a seat belt apparatus employing the same.

The priority application, Japanese Patent Application No. 2007-229006, filed Sep. 4, 2007 including the specification, drawings, claims and abstract, is incorporated herein by reference in its entirety.

Given the disclosure of the application, one versed in the art would appreciate that there may be other embodiments and modifications within the scope and spirit of the application. Accordingly, all modifications attainable by one versed in the art from the present disclosure within the scope and spirit of the present application are to be included as further embodiments of the present application. The scope of the present application is to be defined as set forth in the following claims 

1. A seat belt retractor for winding up a seat belt comprising: a spool for winding up the seat belt; a locking mechanism that allows the rotation of the spool when the locking mechanism is not in operation and prevents rotation of the spool in a belt withdrawing direction when the locking mechanism is in operation; a belt withdrawal sensor that is actuated when the seat belt is withdrawn at a speed higher than a normal speed at a start of the withdrawal of the seat belt, and; a lock actuation mechanism that actuates the locking mechanism based on the actuation of the belt withdrawal sensor, wherein the lock actuation mechanism comprises at least a lock gear that rotates together with the spool when the lock actuation mechanism is not in operation and rotates relative to the spool when the lock actuation mechanism is in operation, the lock gear actuating the locking mechanism by the relative rotation between the lock gear and the spool when the lock actuation mechanism is in operation, and wherein the belt withdrawal sensor is disposed on the lock gear allowing the belt withdrawal sensor to oscillate between an inoperative position where the belt withdrawal sensor allows the rotation of the lock gear both in the belt winding direction and the belt withdrawing direction and an operative position where the belt withdrawal sensor prevents the rotation of the lock gear at least in the belt withdrawing direction, the seatbelt retractor further comprising: an oscillation preventive member for preventing the oscillation of the belt withdrawal sensor and an oscillation preventive member control mechanism for controlling the movement of the oscillation preventive member, wherein the oscillation preventive member is movable in a radial direction through a rotational center of the spool between an oscillation preventing position where the oscillation preventive member holds the belt withdrawal sensor at the inoperative position to prevent the belt withdrawal sensor from oscillating toward the operative position at least when the seat belt is fully or nearly fully wound, and an oscillation allowing position where the oscillation preventive member allows the oscillation of the belt withdrawal sensor when a certain amount of the seat belt is withdrawn from the fully wound state, and wherein the oscillation preventive member control mechanism comprises a movement control member that rotates at a speed lower than the speed of the spool to control the movement of the oscillation preventive member when the spool rotates.
 2. A seat belt retractor as claimed in claim 1, further comprising: an emergency locking mechanism that detects a vehicle deceleration larger than a normal deceleration and actuates to prevent the spool from rotating in the belt withdrawing direction; an automatic locking mechanism that is actuated when the seat belt is fully withdrawn and prevents the withdrawal of the seat belt during winding after the seat belt is fully withdrawn until a certain amount of the seat belt is wound; and a lock switching mechanism for switching between an emergency locking function mode in which an emergency locking function is executed by the emergency locking mechanism and an automatic locking function mode in which an automatic locking function is executed by the automatic locking mechanism, the lock switching mechanism comprising: a switching lever that is selectively set at either of an emergency locking position where the emergency locking function mode is set or an automatic locking position where the automatic locking function mode is set, and an eccentric gear that rotates when the spool rotates, the eccentric gear rotating at a speed lower than the rotational speed of the spool and comprising a switching lever control cam member for switching the setting position of the switching lever, wherein the movement control member comprises the eccentric gear and the oscillation preventive member is a member of which movement is controlled by the rotation of the eccentric gear to prevent the actuation of the belt withdrawal sensor when the seat belt is fully or nearly fully wound.
 3. A seat belt retractor as claimed in claim 2, wherein the belt withdrawal sensor comprises a ring member and the oscillation preventive member comprises a plurality of stoppers that press an inner periphery of the ring member to prevent actuation of the belt withdrawal sensor when the seat belt is fully or nearly fully wound.
 4. A seat belt retractor as claimed in claim 3, wherein the stoppers comprise a stopper biasing member for biasing the stopper in a direction pressing against the ring member.
 5. A seat belt apparatus comprising: a seat belt for restraining an occupant; a seat belt retractor for winding up the seat belt while allowing withdrawal of the seat belt, the seat belt retractor being actuated in the event of an emergency to prevent the withdrawal of the seat belt; wherein the retractor comprises a spool for winding up the seat belt; a locking mechanism that allows the rotation of the spool when the locking mechanism is not in operation and prevents rotation of the spool in a belt withdrawing direction when the locking mechanism is in operation; a belt withdrawal sensor that is actuated when the seat belt is withdrawn at a speed higher than a normal speed at a start of the withdrawal of the seat belt, and; a lock actuation mechanism that actuates the locking mechanism based on the actuation of the belt withdrawal sensor, wherein the lock actuation mechanism comprises at least a lock gear that rotates together with the spool when the lock actuation mechanism is not in operation and rotates relative to the spool when the lock actuation mechanism is in operation, the lock gear actuating the locking mechanism by the relative rotation between the lock gear and the spool when the lock actuation mechanism is in operation, and wherein the belt withdrawal sensor is disposed on the lock gear allowing the belt withdrawal sensor to oscillate between an inoperative position where the belt withdrawal sensor allows the rotation of the lock gear both in the belt winding direction and the belt withdrawing direction and an operative position where the belt withdrawal sensor prevents the rotation of the lock gear at least in the belt withdrawing direction, an oscillation preventive member for preventing the oscillation of the belt withdrawal sensor and an oscillation preventive member control mechanism for controlling the movement of the oscillation preventive member, wherein the oscillation preventive member is movable in a radial direction through a rotational center of the spool between an oscillation preventing position where the oscillation preventive member holds the belt withdrawal sensor at the inoperative position to prevent the belt withdrawal sensor from oscillating toward the operative position at least when the seat belt is fully or nearly fully wound, and an oscillation allowing position where the oscillation preventive member allows the oscillation of the belt withdrawal sensor when a certain amount of the seat belt is withdrawn from the fully wound state, and wherein the oscillation preventive member control mechanism comprises a movement control member that rotates at a speed lower than the speed of the spool to control the movement of the oscillation preventive member when the spool rotates. a tongue slidably supported by the seat belt, and a buckle fixed to a vehicle floor or a vehicle seat and to which the tongue is detachably latched. 